This invention relates to a transmission control circuit and more particularly, to a transmission control circuit for an electronically controlled automatic transmission which utilizes a transmission range sensor operatively ganged with one or more electrical switches which selectively enable and disable the transmission""s solenoid valves.
Transmission systems typically include one or more solenoid valves which are used to selectively activate and deactivate the transmission clutches through one or more hydraulic circuits. Particularly, a controller selectively activates and deactivates the solenoid valves based on various inputs, such as vehicle speed, engine speed and torque, gear selector or xe2x80x9cshifterxe2x80x9d position and other inputs. Once activated, the selected clutches switch gears by use of hydraulic pressure. Conventional transmissions further include a hydraulic manual control valve which selectively enables and disables the various hydraulic circuits which power the clutches. The use of the hydraulic control valve protects against damage which could otherwise be caused by unwanted solenoid activation which may occur in the presence of electronic malfunctions and system failures. Particularly, the hydraulic control valve disables certain hydraulic circuits based upon the position of the gear selector, thereby ensuring that certain clutches cannot be inadvertently activated, even if their respective corresponding solenoids are errantly energized.
Due to the advancement of electronic controls in automatic transmissions, the integrity of the electrical system is becoming increasingly critical for proper transmission robustness. Many such modern transmissions which utilize direct electronic solenoid control could eliminate the hydraulic manual control valve altogether. However, these systems would require redundancies in the transmission range sensing and processing systems as well as additional high and/or low side solenoid driver circuits to guard against unwanted solenoid operation. These additional systems and components would undesirably increase the cost and complexity of the transmission system and would not provide the same integrity and robustness of a hydraulic manual control valve.
There is therefore a need for a new and improved transmission control circuit which overcomes at least some of the drawbacks of prior systems and which includes one or more high current electrical switches which are operatively connected to or xe2x80x9cgangedxe2x80x9d with a low current transmission range sensor.
It is a first object of the invention to provide a transmission control circuit which overcomes some or all of the previously delineated drawbacks associated with prior circuits and systems.
It is a second object of the invention to provide a transmission control circuit including one or more high current electrical switches which selectively enable and disable several transmission solenoid valves, and a low current transmission range sensor which is operatively ganged with the high current electrical switches and which provides a signal which is used to control the solenoid valves.
It is a third object of the invention to provide a transmission control circuit which includes several high current switches which are operatively connected to the transmission gear selector and which selectively connect and disconnect the transmission solenoid valves to the battery based upon the position of the gear selector.
According to a first aspect of the present invention, a control circuit is provided for use with an electronically controlled transmission system of the type having a gear selector, at least one control solenoid and a source of electrical power. The control circuit includes a transmission range sensor which is communicatively coupled to the gear selector, which senses a position of the gear selector and which generates a signal based upon the sensed position; at least one electrical switch which is operatively coupled to the gear selector, to the source of electrical power and to the at least one control solenoid, the at least one electrical switch being effective to selectively connect and disconnect the at least one control solenoid from the battery based upon the position of the gear selector; and a controller which is communicatively coupled to the transmission range sensor and to the at least one control solenoid and which is effective to receive the signal and to cause the at least one control solenoid to be selectively energized and de-energized based upon the signal.
According to a second aspect of the present invention, a method is provided for controlling a transmission system of the type having a battery, a selectively positionable gear selector and a plurality of control solenoids. The method includes the steps of providing a plurality of electronic switches; operatively coupling each of the plurality of electrical switches between the battery and a unique one of the control solenoids; and operatively coupling each of the plurality of electrical switches to the gear selector effective to cause the plurality of electrical switches to selectively connect and disconnect the plurality of control solenoids to and from the battery based upon the position of the gear selector, thereby selectively enabling and disabling the plurality of control solenoids.
These and other features, advantages, and objects of the invention will become apparent by reference to the following specification and by reference to the following drawings.